The invention relates to submarine cables and, more particularly, to repeatered submarine cables adapted for broadband communication.
The well-known broadband characteristics of optical fibers, together with the relatively few repeaters per given distance which they require in a transmission system of significant length, make such fibers a prime candidate for intercontinental and other undersea communications. This, of course, requires the incorporation of the fiber system into a submarine cable.
One major problem inhibiting the use of optical fibers in a submarine cable is the necessity of hermetic protection of the fibers against moisture. This is particularly significant because of the mechanical stresses on a submarine cable during laying and recovery, since the combination of moisture and stress on an optical fiber has been found to quickly lead to structural failure. Moreover, a fiber-bearing cable must provide an efficient DC path for powering the optical repeaters in the system and must be sufficiently strong to withstand the above-mentioned stresses and years of operation at sea.
The reconciliation of these requirements in a single submarine cable has up to now been elusive. For example, while certain manufacturers presently offer multielement optical fiber arrays which are arranged in cable form (including strength members and packing), such designs cannot reliably withstand the pressures and stresses of operation at sea, nor are they sufficiently waterproof to prevent deleterious moisture penetration to the fibers.